Apparatus for producing magnetic records on tape



March 22, 1960 T. R. GARRITY 2,929,670

- APPARATUS FoR PRonucING MAGNETIC REcoRDs oN TARE original Filed oct. 22. 1952 im\73 |77 v l .'5 Sheets-Sheet l THOMAS R. GARRITY ATTORNEY March 22, 1960 T. R. GARRITY APPARATUS FOR PRODUCING MAGNETIC RECORDS 0N TAPE Original F'ild 0G13. 22. 1952 3 Sheets-Sheet 2 F IG. 4

THOMAS R. GARRITY ATTORNEY March 22, 1960 T. R. GARRITY APPARATUS FOR PRODUCING MAGNETIC RECORDS ON TAPE Original Filed Oct. 22, 1952 3 Sheets-Sheet 3 F|G.7c

FIG.7G

AAAA VVV AL YV FlG.7br

INVENTOR THOMAS R. GARRITY APPARATUS FOR PRODUCING MAGNETIC RECORDS ON TAPE Thomas R. Garrity, Wappingers Falls, N.Y., assigner to international Business Machines Corporation, New York, Fifi., a corporation of N ew Yori;

Griginai appiication October 22, i952, Seria! No. 316,247. Divided and this application November 12, 1958, Serial No. 773,429

7 Claims. (Cl. 346-74!)V This invention relates to means for making magnetic control records for record controlled machines, this application being a division of my application for United States patent, Serial No. 316,247, led October 22, 1952 for Magnetic Tape and Method for Producing Record Thereon, now abandonded.

it is an object of the invention to provide means for producing a control record having magnetic spots capable of producing distinctly dilerent responses in a sensing device, depending upon the novel arrangement and diierentiating characteristics of the spots.

it is a further object of the invention to provide means for producing a magnetic record of great information densities.

These and other objects of the invention are attained by roviding a magnetic recording head having a plurality of recording gaps which are disposed in angular relation to each other such that record spots can be produced in diagonal relation to an axis of the record body. It is also a purpose of this invention to provide a recording head of the kind herein disclosed which can also be utilized to produce a record having crossed spots, the magnetic axes of which are angularly arranged in relation to each other.

The invention further contemplates a control system for a recordinghead capable of producing bipolar magnetic spots on a record body, such as that indicated, whereby the magnetic spots are further differentiated. l

In pulse or magnetic spot recording on magnetic record bodies, there are definite restrictions which limit the in formation density. in any given magnetic recording systern, the information density is a function of the number ci spots per unit length of the recordbody, and the number of tracks, or magnetized strips on such body. The restrictions as to the number of spots per unit length of a record body are imposed because of the fact that, as the density of the spots is increased beyond a certain point, such spots begin to demagnetize each other. Therefore, a definite spacing between spots within a track must be maintained. As magneto motive force used in applying the spots to the record body is increased, the spacing between adjacent spots must be increased correspondingly to avoid the demagnetizing effect. On the other hand, spacing between strips or tracks of spots made on a single record body must likewise be maintained for the same reason, e.g., because the spots when applied to a magnetic record body set up a flux pattern which spreads not only longitudinally along a record body, i.e., between successive spots, but the flux also spreads out laterally across the record body. Therefore, a spacing between adjacent tracks or strips of spots on a single record body must be maintained in order to avoid interference between spots ci adjacent tracks. Such interference is not only that ot dcmagnetization, but also the fact that when the record body is being read, if insufficient spacing is maintained, the magnetic spots on one track cause interference during the reading of an adjacent track of the record body.

`Accordingly, it is a specific object of the invention to nite States atent rice provide a magnetic recording head which will record magnetic spots such that interference between adjacent tracks of magnetic spots on a record body is avoided. This is accomplished by utilizing a multi-gap recording head in which the gaps are disposed in angular relation to each other such that when recording, the spots of one track are disposed diagonally to an axis of the record body while the spots of an adjacent track are disposed on the opposite diagonal.

Another specific object of the invention is to provide means for superimposing diagonally applied magnetic spots upon the same strip or track of a record body, one group of spots being applied with their axes lying along one diagonal and the other group being applied with their Xes lying along the opposite diagonal.

A further specific object of the invention is to provide a multi-characteristic spot recorder and to teach a method and means of using multi-characteristic spots produced thereby in magnetic recording.

One manner in which these and other objects may be attained will appear from the detailed description in which the record body on which the recording head is shown to operate will be referred to as a tape.

In the drawings Fig. l is a perspective view of a combined spot recording head showing the electrical circuit for its coils;

Fig. 2 is a schematic illustration of a magnetic tape Vshowing the orientation of lines of ux when two sets of magnetic spots are superimposed;

Fig. 3 illustrates a fragment of a magnetic tape con` taining a number of tracks or strips and illustrates the increase in number ci tracks which may be attained by this invention;

Fig. 4 illustrates a series of enlarged views of the face of a multiple characteristic spot read-write head showing the various combinations of multiple characteristic spots which may be obtained by use of the multiple characteristic spot recorder;

Fig. 5 is an electric bridge circuit which is analogous to the magnetic circuit of the multi-characteristic spot head;

Fig. 6 is an electric circuit showing the path or" current ilow for purposes of calculation; and

Figs. 7a-7d show four bridge lcircuits which are to be superimposed to determine conditions of current how.

As set forth in the stated objects, onerof the methods of this invention results in doubling the information density on a tape, i.e., the number of magnetized spots per unit length of tape, by means of orienting the magnetic axis of each spot at an angle of about 45 with the longitudinal axis of the tape. One type of mag'- netized spot here contemplated is a bipolar spot in a strip of permanently magnetizable material. Such a magnetic spot will have an axis which runs through the north and south poles of the permanently magnetized spot, and will have a polarity characteristic depending upon the relative location of the north and south poles with respect to one another. The magnetic axis or the spot will be at right angles to the gap in the head which formed the spot, because the lines of force of the magnetic iield which form the spot take the shortest path, viz. at right angles to the gap. Each magnetic spot as formed in a tape has directional as well as polarity characteristics, the lines of force largely lying in parallel relation in a direct path between the northand south poles. Hence, the aXisof a spot will be the center line joining the centers of the north and the south pole areas. The polarity characteristic of these magnetic spots depends upon the location of the magnetic poles as mentioned above, because the direction of flow of electric current in a pick-up head is dependent upon the familiar rules of electromagnetic induction, and therefore the l current induced in the pick-up head will be reversible in of strip 11. This orientation is schematically illustrated VV-bymeans of slanted Ybars 13.

Since, when the tape is jacent tacks are oriented at right angles to each other.

being read, the pick-up head is substantially insensitive v to linesV of flux which are parallel to the gap of the pickup head, only thoselines of flux lying at right angles Yto the `gap will aiTect the pick-up head and produce a signal. Therefore, if the strip ofvtape 11 is magnetized with a series of spots having their magnetic axes slanted,

as illustrated by bars 13, a second series of spots hav-V ling their magnetic axes slanted on the opposite diagonal or at about 45 in the other direction with respect to the llongitudinal axis of strip 11 (as illustrated by slanted bars 15) may be superimposed on the same area of tape -11. Therefore, double the number ofY spots may be ap- Yofi-spots will affect a reading head placed at a given diagonal. Although there will be areas vwhere`the lines A, of flux Vhaving a high density will cross one'another as is illustrated by the schematic bars 13 and 15, and these areas will be magnetically saturated, the areas between the saturated points, however, will be able to supply the necessary lines of force to produce a signal. Y v Another `method vby which the information density may be at least doubled, is that illustrated by Fig. 3 where a strip of magnetic tape 17 has applied thereon a numberY of tracks. Using the principles of this invention, every alternate track 19, 21, 23, 25, 27, 29 and 31 ,may be magnetized with spots having their magnetic axes lying diagonally to the edge or longitudinal axis of tape 17. Tracks 33, 35, 37,Y 39, 41 and 43, lying between the aforesaid alternate tracks, may be magnetized with spots having their magnetic axes lying along the opposite diagonal or at about 90 to the axes of the spots on the tracks 19, 21, etc.

It may'b'e'pointed Yout that the increase in the number of tracks on tape 17, according to this Slater method,

is possible because no interference is developed 'between adjacent tracks, the lines of ux havingY been set upat right angles to one another in such adjacent tracks.` The slant lines shown lying in eachV of thetracks 19 through 43 illustraterthe orientation of the magnetic axes of the spots which are applied along each track.v

It will be appreciated that any appropriate type of magnetic spot-forming writing head `may be used to apply the spots to the magnetic tape in the methods as described with reference to Figs. 2 and 3, one such writing head being described and shown in the aforementioned. patent to Robert I. Roth. Y

An important feature of the invention lies in the orientation of the magnetic spot-producing head with its gap lying at a diagonal or'approximately 45 in one di rection or the other in relation to the longitudinal axis of the magnetic tape. It will be appreciated that with respect to the superimposed spot method illustrated by Fig. 2, it would not be necessary to have the axes of the spots lie diagonally with respect to the tape so Vlong as the axes of each series of spots are placed at right angles to the axes of the other series upon which the second series is superimposed. I Y

With respect to the method of increasing the number of tracks as illustrated in Fig. 3, the 'illustrated `diagonal orientation of the spots in relation to the tape need not necessarily be maintainedsolong. as the spots of-ad- -by means of reversingswitches 71.

However, the most efficient use of the available area on the tape becomes possible-'by using the diagonal orientation of the spots with reference to the axes of the tape since closer spacing of'the successive spots in each track is possible with this arrangement. Y

In Fig. 1 there is illustrated la combined multiple characteristic spot-producing head 45 shown in juxtaposition with a strip of tape 47. The multiple spot-producing head 45 may be constructed with four separate magnetic paths made up of a group of magnetic material legs 49, 51, 53 and 55.V TheseV legs are joined at the top in intimate contact. ,Their intersection forms an X shaped pattern 57 although any desirable intimate Acontact pattern may be employed.

A the bottom of the multiple spot head 45, the legs 49, 51,53 and 55 are joined to form a square'or rectangular 'face 59 which has a 'set of gaps 61 in the shape of an X. The gaps 61 are preferably formed by a thin copper shim disposed between the adjacent faces of the intersection of legs 49, 51, 53 and 55.

The formation of a magnetic spot will be accomplished in a well-known manner by the energization of agroup of coils 63, 65, 67 and 69. Energization of these coils may be accomplished with any appropriate source of direct current, and is effected with reversible polarity, e.g. In producing this type of magnetic spot,'aV very satisfactory vmeans of energizationgof coils 63, 65, 67 and 69 for a short duration 'and with a ratherrhigh current ow, may be such as that illustrated by use of a battery 73 and a single pole doublethrow switch 75 in connection with a condenser 77. The condenser77`will be charged by throwing the switch 75 Vto the position shown in Fig. l and then, after setting the reversing switches 71 in adesired combination of positions, switch,75 will be thrown to the opposite position, where it will open the circuit of battery 73 and 'producing a magneto-motive force in 'each of the four legs 49, 51, 53and 55 which will.V in turn, magnetize the spot on tape 47 which is then adjacent to the face area v59 of the four magnetic materialY legs 49"through 55.

It lwill be noted that the reversing switches 71 may vbe closed in a variety of combinational patterns, and because of the vector or directional properties of a magnetic spot as produced by this type of magnetic writing head, a multiple characteristic magnetic spot may be thereby yproduced on the tape.

The variously differentiatedspots which may be produced by means of the multiple spot head 45 are illus trated in Fig. 4. In Fig. 4 each square represents the face 59 of the magnetic spot head 45 and the small arrows within the squares illustrate the direction of the ux which is produced by the energization of the coils 63 through 69 in one direction or the other as determined by the combinational setting of reversing switches 71 prior to the discharging of condenser 77 by throwing switch 75 to its discharge position. Polarities of the magnetic flux paths of the four legs 49, S1, 53 and 55 are indicated by plus.(|) and minus signs. Plus may be assumed to represent a north pole. It will be observed that whenever adjacent legs of the head 45 have the same polarity, no ux tends to ow between such legs. In the case where` three of the legs have the same polarity, it will be observed that all ofthe flux is illustrated as passing from the fourth leg having opposite polarity to or from its adjacent two legs only. The reason'for this will be apparent upon investigation ofthe electrical analogy. However, it will be suicient to point out that the amount efflux which tends to ow to the non-adjacent leg is only about 5% of that owing to adjacent legs.

lt will be observed that it is possibleto produce spots having fourteen (14) diierent characteristics with a single spot-producing head 45. It will be appreciated that by using the spot-producing head 45 as a pick-up or reading device, a different characteristic signal for each of the fourteen characteristic spots ona tape being read, may be produced. For example, volt meters might be connected across each of the four coils 63, 65, 67 and 69. Then when the tape 47 with spots already impressed thereon is moved rapidly across the face 59 of multiple head 45, a given combination of voltages of one polarity or the other would be induced in the coils 63-69 and hence would register correspondingly on the volt meters.

Fig. illustrates an electric bridge circuit which is analogous to the magnetic circuit of multiple spot head 45. In order to show the ux distribution at the four gaps between legs 49 to 55, we will assume that the magneto-motive force applied by the coils 63 through 69 is the counterpart of voltage sources 79 illustrated in Fig. 5. Assuming that the resistances illustrated in Fig. 5 are the counterpart of the reluctances involved in the multiple spot head 45, and assuming the reluctance of each gap 61 is ten times greater than the reluctance of each magnetic material leg, e.g. 49, and also assuming that the reluctance of the points of intimate contact 57 is five times that of each magnetic material leg (e.g. 49), we may assign a resistance value of R to the diagonal resistors illustrated in Fig. 5. The resistors on the outside of the square illustrated in Fig. 5 will be the counterpart of the intimate contact areas 57 and will therefore be 5R as shown in Fig. 5. The resistors on the inner square represent the reluctance of the gaps 61 and are therefore given a value of R as illustrated. In order to calculate the current distribution through the lOR resistors, we may assume that three of the voltages 79 are short circuited and that the remaining voltage has a magnitude such that 100 amperes will iiow through the adjacent diagonal resistor R. Then by laying out the current path from a corner point S1 to a point 83 (assuming current ow from plus to minus and assuming corner point Si to be on the plus side of voltage 79) in a parallel path circuit diagram as illustrated by Fig. 6, the calculation of current ow in the individual legs will be as follows: by inspection, the current distribution may be found to be that illustrated in Fig. 6, i.e., starting with 100 amperes, dividing to 50 amperes in each branch, then each branch shunting oft` an unknown current iiow i which rejoins its branch to make the branch current of 50 amperes again and nally the branches join to iiow through the single diagonal resistor R at 100 amperes. The arrows indicate the direction of current iiow. Now, by equating Vthe IR voltage drops to the driving voltage E (source 79) we get the following equations:

(1) ZSOR-I-SR-l-2Ri-l-l0Ri-i-50OR-I-100R=E (2) 250R+5ORR1`|500R+100R=E reducing Equations l and 2 gives: (1) SSOR+17Ri=E (2) Soca-Riza subtracting Equation 2 from Equation l and solving for i, gives:

*5G rit-.L38 Rfi=9 Now, by inserting the value of i in Fig. 6, the various currents may be found. Then by superimposing the currents caused by the four voltages 79, depending upon their polarities, the currents in the lOR resistors may be found. The analogous ux distribution will thus be determined. For example, taking the case when one of the reversing switches 71 is set for one direction of current ow and the other three switches 71 are set for the opposite direction, then the analogous current ow may be found be superimposing the four bridge circuits illustrated in Fig. 7 which gives currents of 100 amperes in the two adjacent IOR legs (analogous to gaps 61) and currents of 5.56 amperes in each of the other two IOR legs. It will be noted that the current distribution is such that the opposite leg (the one which has an cpposite polarity compared to the other three) carries about 5% of the current flowing in each of theadjacentV legs. This then bears out the statement concerning tiux distribution which was made previously.

It will be observed that the current ilow which is effected through the four resistors lOR is distributed so as to produce relative values which are the same as the relative strength of the flux produced across the four gaps 61-by the multiple head 45.

From the above description it will be apparent that by using a multiple spot head such as that disclosed in accordance with this invention a multiple characteristic magnetic spot may be produced, the character of which in the case of a head having four legs such as that illustrated in Fig. l will produce spots having fourteen distinct characteristics. These fourteen different characteristic spots are illustrated in Fig. 4, where the symbols stand for a north magnetic pole and signs stand for a south magnetic pole and assuming ux ow from north to south. In former practice a magnetic spot could have but two characteristics depending upon its polarity.

While I have disclosed speciiic embodiments of my invention which are preferred, it is clear that similar embodiments might be had which are within the scope of the ordinary skill of a journeyman in the art. Therefore, my disclosure should not be taken in a limiting sense but merely as descriptive.

I claim:

1. In a magnetic recording head adapted to recording of the spot characteristic type, means providing at least three magentic material paths, each said paths having an electromagnetic coil for producing magnetic ux therein, circuit means for energizing said coils with a given direction of current ow, and linear transducing gaps in said magnetic paths which intersect at a common point, said gaps being diagonally situated with respect to each other.

2. In a magnetic recording head adapted to recording of the spot characteristic type, means providing four legs of magnetic material, each having a coil wound thereon, circuit means for energizing said coils to produce magnetic flux in said legs, said legs meeting at a common area to form four transducing gaps adjacent to the path of a record body, said gaps all meeting at a common point and being situated diagonally with respect to each other.

3. In a magnetic recording head adapted to recording of the spot characteristic type, means providing four legs of magnetic material, each having a coil wound thereon, circuit means for energizing said coils simultaneously to produce a magnetized spot on a record body, said legs all meeting in intimate contact at a common point to complete a magnetic path for each leg, said legs meeting at a face area to form transducing gaps for location close to a record body, said gaps all being straight line in character and intersecting as an X at a common point, said gaps being situated diagonally with respect to an axis of the record body path.

4. A multi-characteristicmultipolar spot read-write head comprising means providing at least three magnetic material paths, each said paths having an electromagnetic coil for producing magnetic flux therein, said magnetic paths having transducing gaps which intersect at a common point, and means for selectively energizing said coils with a given direction of current.

5. A multi-characteristicl multipolar spot read-write head comprising means providing at least three magnetic material paths, each said paths having an electromagnetic coil for producing magnetic iiux therein, circuit means head comprising means providing four-legs of magnetic material, each having a coil wound thereon, circuit means Vfor reversibly' energizing said coils in a selected combination vof directions, said legs meeting at a common'area to form fourtransducing gaps adjacent to thepath of a record bodyysaid gaps all meeting at a common point and being situated diagonally with respect to eachnotherw v ,7. A multi-characteristic multipolar Vspot read-write head comprising four legs of magnetic material, each said legs having a coilY wound thereon,Vv circuit means for reversibly energizing' said coils simultaneously :in a selected Acombination ofdirections'to produce a corresponding selected polarity effect on the spotVV being recorded,

said legs all meeting in intimate contact at a common point tocomplete a magnetic path for each leg, Vsaidlegs meeting at a face area to form gaps transducing for location close to a recording station to magnetize -a`spot on, a record body in such station; said gaps all being straight line inv character and intersecting Vas. an X at -aV common point, said gaps being situated diagonalliI with vrespect'to Aan axis of the record 'body' patht References Cited in the file of this patent UNITED STATESVPATENTS A A 2,548,109 Howey .-.l Apri 10, "2,573,248 A Hamberg ..v n 'Mar.- 23; 1954 42,709,073 Kleis Jan. 18, 195'5 "2,803,708

Camras Aug. 20,A 1957 UNITED STATES PATENT oFFTCE CERTIFICATE 0F CORRECTION Ratent No- 2q929v670 March 22, 1960 Thomas R., Garrty It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 line 1Y for "tacks" read tracks --j line 16, for "A the" read At the column 8., line l.Y for "gaps transducng" read transducng gaps Signed and sealed this 20th day of September 1960.

(SEAL) Attest:

KARL HB AXLINE RBERT C. WATSON Attesting @Hicer Commissioner of Patents 

